1. Technical Field
The present invention relates to a method of manufacturing a semiconductor device that includes two transistors having side wall spacers with different widths.
2. Related Art
In recent years, a system LSI has been used in which a series of functions are integrated into one semiconductor device. In many cases, a logic unit and a memory, such as a SRAM or a DRAM are provided in the semiconductor device.
In the semiconductor device, the gate side wall spacers of the logic unit and the DRAM have the same structure. However, with the miniaturization of elements, it has been difficult to meet the required characteristics in the same side wall spacer structure. Therefore, it is necessary to form the side wall spacers with different widths in the logic unit and the DRAM.
For example, Japanese Unexamined patent publication NO. 2005-005508 discloses a method of manufacturing a semiconductor device shown in FIGS. 9 to 16. First, as shown in FIG. 9, a first gate electrode 3a and a second gate electrode 3b are formed on a silicon substrate 1 having an element isolation oxide film 2 formed thereon. Then, a silicon oxide film 4 serving as a first etching stopper layer, a silicon nitride film 5 serving as a second etching stopper layer, and a silicon oxide film serving as a first side wall spacer layer 6 are sequentially formed thereon.
Then, as shown in FIG. 10, the entire surface of the first side wall spacer layer 6 is etched back by an anisotropic etching method such as a dry etching method. In this case, the etching conditions have high selectivity with respect to the silicon nitride film 5. Therefore, the silicon nitride film 5 remains and the silicon oxide film 4 is protected.
Then, as shown in FIG. 11, a photoresist film 7 is formed, and a groove is formed in the photoresist film 7 to expose the gate electrode 3b and the periphery thereof.
Then, as shown in FIG. 12, the first side wall spacer layer 6 formed on the side surface of the gate electrode 3b is removed by wet etching.
Then, as shown in FIG. 13, the photoresist film 7 is removed by an ashing apparatus or a wet etching apparatus.
Then, as shown in FIG. 14, the silicon nitride film 5, which is the second etching stopper layer, is removed by dry etching or wet etching. This etching is performed under the conditions that have high selectivity with respect to the silicon oxide film 4.
Then, as shown in FIG. 15, a silicon oxide film 8 is formed. Then, as shown in FIG. 16, anisotropic etching, such as dry etching, is performed on the silicon oxide film 8 to form a side wall spacer layer. Side wall spacers with different widths can be formed on the gate electrodes 3a and 3b by the above-mentioned processes.
Japanese Unexamined patent publication NO. 2004-349680 discloses a semiconductor device which includes a first field effect transistor forming a non-volatile memory cell and a second field effect transistor forming a circuit and in which the side wall spacers in the first field effect transistor and the second field effect transistor have different widths. Specifically, a laminated film of a silicon oxide film, a silicon nitride film, and a silicon oxide film formed in this order is formed on a gate electrode of the first field effect transistor and a gate electrode of the second field effect transistor. Then, etching is performed using the silicon nitride film as an etching stopper to selectively remove the uppermost silicon oxide film from the gate electrode of the second field effect transistor. Then, etching is performed on the laminated film to form a side wall spacer.
The present inventor has recognized as follows. In the techniques disclosed in Japanese Unexamined patent publication NOs. 2005-005508 and 2004-349680, anisotropic etching, that is, dry etching is performed on the laminated film, with the etching stopper, which is the silicon nitride film, left, to form the side wall spacer. Therefore, when the etching stopper film is removed, a predetermined amount of silicon oxide film forming a main portion of the side wall spacer with a large width is removed. Therefore, it is difficult to form the side wall spacers with significantly different widths.